Conventionally, mobile phones, PDA (Personal Digital Assistant) terminals or other electronic devices include plural wiring boards on which printed wirings are formed and a number of electronic parts are mounted. The wiring boards are generally connected each other via a connector or using a connecting medium such as solder.
In recent years, the electronic devices have high-functionality and multifunctions. Plural printed wiring boards including a number of electrode terminals for connection should be connected. The electrode terminals are often disposed in a matrix array in the printed wiring board (the matrix array herein means that the electrode terminals are systematically, not always orthogonal, arranged in a matrix).
In the conventional electronic device, an example of the circuit board device including plural wiring boards connecting each other has a configuration that electrode (signal) terminals arranged in the matrix array on respective wiring boards can be connected. The circuit board device is a most general-purpose type such that two printed wiring boards are connected via a connector. Specifically, a convex (male) connector is attached as a connecting part at the predetermined portion of one printed wiring board, and a concave (female) connector is attached as a mating connecting part at the predetermined portion of the other printed wiring board. The electrode terminals on the respective printed wiring boards are electrically connected each other by fitting the connectors.
Japanese Unexamined Patent Application Publication No. 2002-56907 (FIG. 3, page 4, hereinafter referred to as Reference No. 1) discloses a circuit board device including plural wiring boards in the conventional electronic device that electrode (signal) terminals arranged in a matrix array on the wiring boards can be connected. The circuit board device comprises a first wiring board having plural first electrode terminals 33 for connection row-arranged on a surface layer, a second wiring board having plural second electrode terminals for connection row-arranged on a surface layer, and a square pole-shaped anisotropic conductive member disposed between the first wiring board and the second wiring board into which metal terminals are embedded corresponding to the positions of the electrode terminals. Specifically, vias are formed on the first electrode terminals of the first wiring board to draw wiring patterns onto an inner layer, vias are also formed on the second electrode terminals of the second wiring board to draw wiring patterns onto an inner layer, and the anisotropic conductive member is disposed between the first wiring board and the second wiring board to provide the laminated circuit board device. The electrode terminals of respective wiring boards are electrically connected each other via the metal terminals embedded into the anisotropic conductive member.
In this regard, in any of the conventional circuit board devices described above, the wiring boards are easily separated each other, whereby the wiring board can be replaced if an electronic part to be mounted is defective.
Similarly, it is known that electrode (signal) terminals arranged on a wiring board can be connected in a circuit board device including plural wiring boards in the conventional electronic device. The circuit board device is a general-purpose type that a flexible print wiring board having a connect portion is directly connected to a rigid print wiring board via a connecting means. Specifically, the electrode terminals of the flexible printed wiring board and the rigid printed wiring board are connected using a connecting medium such as solder, ACF (Anisotropic Conductive Film), ACP (Anisotropic Conductive Paste) and the like to provide the circuit board device. Thus, the electrode terminals of the flexible printed wiring board and the rigid printed wiring board are electrically connected via the connecting medium. When the solder is used as the connecting medium, typical solder generally used for mounting the electronic parts to the wiring board can be used. Before the wiring boards are connected, a solder paste may be applied to the electrode terminals of the wiring board to fix the boards temporarily, and the connected parts may be heated and pressed to connect and fix the wiring boards. When the ACF or the ACP is used upon the connection of the wiring boards, a film or a paste may be sandwiched between the electrode terminals to be connected, and heated and pressed to connect and fix the wiring boards as in the case of using the solder, since the ACF is a film-like form comprising an adhesive resin and fine conductive particles and the ACP is a paste-like form comprising the similar materials.
In regard to the applicability of the connecting medium, the solder is advantageously used with low costs because the solder is generally used for mounting other electronic parts. However, the solder liquefies upon the connection to shorten adjacent electrode terminals (conductive patterns) and is therefore not suitable for connecting the terminals with a narrow pitch (in fact, connecting the terminals having 0.3 mm pitch or less is technically difficult). Although the ACF or the ACP invites high costs as compared with the solder, the narrow pitch (even 0.05 mm pitch) can be realized and the ACF or the ACP is therefore generally used for connecting a glass substrate of a crystal liquid display and a crystal liquid driver.
Japanese Unexamined Utility Model Registration Application Publication No. 2-74784 (FIG. 1, claim of utility model, hereinafter referred to as Reference No. 2) discloses a circuit board device including plural wiring boards in the conventional electronic device that electrode (signal) terminals arranged in a matrix array on the wiring boards can be connected. A connector is inserted and mounted into/to a printed board having a guide to fit and contact the connector into/with contact pads having conductive patterns to provide a circuit board device. Specifically, a local portion at one side of the printed board is stepped as a pad plate. Plural contact pads (electrode terminals) are arranged on the pad plate. The guide having concave portions for catching near the local portion at one side of the printed board. One end of the connector having a thickness that is substantially same as that of the printed board has a step-like shape so that a contact plate can be engaged with the pad plate. Plural contacts are disposed under the contact plate such that the contacts are protruded in the same arrangement as the contact pads. Convex portions (spheres are attached to a panel) that apply a force to be caught by the concave portions of the guide are formed. One end of the guide of the printed board is inserted into one end of the connector. The guide is engaged and flushed with the connector in a state that the convex portions of the connector are caught by the concave portions of the guide. Thus, a circuit board device is provided. The contacts are slid and contacted with the contact pads to electrically connect the electrode terminals of the printed board and the connector.
The electrode terminals arranged on the wiring boards of the above-mentioned circuit board devices are evaluated for connection. All circuit board devices described above have the following problems.
The configuration using the solder, ACF, ACP and the like as the connecting medium as described above advantageously realizes a compact body accompanied by slimming and space-saving of the recent electronic devices. In this configuration, the wiring board cannot be easily removed. Therefore, once a defective part is found, all wiring boards including the wiring board to which the defective part is connected cannot be usable (this is noticeable especially when the solder is used), since a probability that a defective part is mounted on a latest-type LSI cannot be ignored (the probability that the defective part is found corresponds to the number of the parts, and the more the parts are, the more the probability increases). As a result, the manufacturing costs undesirably become high due to the defective part.
In contrast, in the configuration using the connector described earlier or using the anisotropic conductive member described in Reference No. 1, each wiring board can be removed. Accordingly, if the defective part is mounted, only the wiring board to which the defective part is connected is removed and replaced with a new one. The problem of an increase in the manufacturing costs caused by the defective part can be advantageously solved or reduced. However, in this configuration, a mounting height becomes high and therefore the compact body cannot be sufficiently realized.
In order to decrease a mounted area of the connection in such a configuration, a configuration of a CSP type substrate and a substrate connector is under review. The electrode terminals of the wiring board to which the connector is mounted are arranged in a matrix array, thereby reducing the mounted area. When respective electrode terminals are arranged in a matrix array for densification, vias are formed on the electrode terminals and the wirings should be drawn into the inner layer. When the vias are formed on the electrode terminals, the surfaces of the electrodes are dented about 15 to 40 μm. Accordingly, mounting the rigid CSP type connector may cause voids and a poor contact at the vias or stress concentration thereby decreasing reliability.
These problems also arise on the circuit board device using the anisotropic conductive material described in Reference No. 1. When the electrode terminals are arranged in a matrix array for densification, the wirings should be drawn into the inner layer. The vias dent the surfaces of the electrodes about 15 to 40 μm. Accordingly, a poor contact is provided at the vias.
Furthermore, in the circuit board device described in Reference No. 2, a contact pressure is produced only by a metal elasticity on a contact formed on a contact plate of the connector that fits into the stepped wiring board. In this case, the contact pressure may be changed depending on a height difference of the steps by the contact plate variations produced. When there are contact-to-contact variations upon the production, the contact pressure may be changed per contact even on the same step. Thus, the contact pads (electrode terminals) on the step are not electrically contacted with the contacts by the uniform contact pressure, resulting in poor connection.
In summary, solving the following problems is desirable: the circuit board device using the anisotropic conductive material described in Reference No 1 becomes high upon the mounting although the increase in the manufacturing costs caused by the defective part can be solved, the poor contact is produced at the vias, and the vias are difficult to be formed.
The present invention is made to solve these problems. An object of the present invention is to provide a circuit board device that can connect wiring boards on which plural electrode terminals for connection are arranged in a matrix array and can be removed and that is easily produced to realize further slimming and space-saving, and to provide a method of interconnecting wiring boards.